1. Field of the Invention
The present invention relates generally to unit assembly structures allowing two units having internal repulsive force after assembly to be assembled against the internal repulsive force, and particularly to assembly structures for a fuser of an image formation apparatus that includes a fusing roll unit having a fusing roll and a pressurizing roll unit having a pressurizing roll and assembled with the fusing roll unit.
2. Description of the Background Art
Image formation apparatuses placing toner on a sheet and heating and pressurizing the sheet with the toner thereon to fuse the toner on the sheet are known in the form of printers, copiers, facsimiles and the like. Such an image formation apparatus has a fuser mounted therein in order to fuse the toner on the sheet. The fuser is typically configured of a fusing roll having a heating function and a pressurizing roll pressed into contact with the fusing roll such that a sheet having toner thereon passes a portion at which the rolls mutually contact.
The above described fuser incorporates a resilient biasing member therein to press the pressurizing roll into contact with the fusing roll. To cause the member to bias, in most cases a load of approximately 10 kgf is required, and this biasing force impairs workability in fabricating the fuser.
To address this, for example, Japanese Patent Laying-Open Nos. 7-84419 and 6-348164 disclose techniques.
Japanese Patent Laying-Open No. 7-84419 discloses a fuser. More specifically, the fuser includes a casing having a main body provided at a side portion with a slit receiving the axes of fusing and pressurizing rolls and the rolls are successively inserted into the slit with a resilient biasing member implemented by a coil spring posed between the fuser's bottom surface and the pressurizing roll's axis, and the casing's lid provided at an upper portion of the casing's main body to be opened and closed as desired is closed to press the fusing roller's axis downward toward the casing's bottom surface, while the lid is locked to the main body to press the pressurizing roll into contact with the fusing roll.
Japanese Patent Laying-Open No. 6-348164 discloses a fuser. More specifically, a casing of a fusing roll unit having a fusing roll incorporated therein and a casing of a pressurizing roll unit having a pressurizing roll incorporated therein are pivotably attached with a pin. The casings have side portions, respectively, notched to receive the rolls' axes. The pair of casings rotates around the pin, and a hook provided at each casing locks the pair of casings with the rolls sandwiched. Note that the hook provided at the pressurizing roll unit is rotatably attached to the casing of the pressurizing roll unit and is also biased by a resilient biasing member implemented by a coil spring. The coil spring's biasing force enables the pressurizing roll to be pressed into contact with the fusing roll with the hook engaging the pair of casings.
As disclosed in the above publications, however, the casings must be pivotably attached by using a pin or the like. This not only renders the casing complex in structure but also contributes to an increased number of components and a cumbersome assembly process. Such can hardly be an assembly structure suitable for mass production.
In assembly a dedicated jig can be used to compress the resilient biasing member or coil spring to prevent the coil spring's biasing force from being an obstacle to the assembly. This, however, requires attaching and removing the jig and hence cannot avoid a cumbersome assembly, and also requires an additional cost for producing the jig.
For unit assembly structures that require two units having internal repulsive force after assembly to be assembled against the internal repulsive force, as described above for a fuser of an image formation apparatus, the internal repulsive force impairs workability in the assembly.